Implications of Carbon Constraints on (1) the Electricity Generation Mix For the United States, China, France and United Kingdom and (2) Future Nuclear System Requirements

Report Date: October 2021
Appendices: No

Abstract

Using the GexX model we determined the average price of electricity for an optimized electrical system as a function of allowable carbon dioxide emissions for Texas (good wind and solar resources), New England (poor wind and solar resources), France, the United Kingdom and two areas of China (low nuclear plant construction costs). Allowable emission rates varied from 500 to 1 g/kWh. Current U.S. carbon dioxide emissions are near 500 g/kWh. The inputs of the GenX model include hourly wind, solar and demand data as well as capital costs, operating costs and operating constraints of each technology. GenX optimizes the system over a period of one year. The capital cost of nuclear power plants was varied to understand the sensitivities in results to the relative cost of nuclear versus renewable energy sources.

In western countries, there were significant increases in the average cost of electricity as tighter carbon dioxide constraints were imposed on the system. In the U.S. with no carbon constraints, natural gas was the low-cost electricity generating option. As carbon dioxide constraints limited the use of natural gas, the optimum system used more wind, solar and then nuclear. There are major changes in the relative amounts of nuclear, wind and solar as a carbon dioxide constraints become more restrictive. The role of nuclear energy changes from traditional base-load nuclear power to variable electricity output—replacing fossil fuels in the role of providing dispatchable electricity at times of low wind and solar output. The relative quantities of wind, solar and nuclear depended upon (1) the quality of wind and solar resources and (2) the cost of nuclear power plants. The exception was China where nuclear energy is the low-cost option; thus, there was little change in electricity costs as carbon constraints became more restrictive. We also modeled the six areas in a scenario where nuclear energy was precluded as an option. This resulted in much higher electricity costs as carbon dioxide emissions became more constrained. Without a dispatchable energy source, one must overbuild wind, overbuild solar and install costly storage systems (batteries and pumped hydro) to replace fossil fuels in their role of providing dispatchable electricity.

Nuclear, wind and solar have high capital costs and low operating costs. In low-carbon scenarios, costs are driven by the need to provide assured electricity generating capacity (kW) more than by the need to provide energy (kWh). We then examined the implications for nuclear energy in this low-carbon world, including several emerging technologies that broaden the use of nuclear energy beyond its traditional role in electricity production.

Nuclear energy with heat storage. The GenX model used current capabilities of nuclear power plants including load following with variable electricity to the grid but did not treat the emerging option of heat storage coupled to nuclear power plants. In a carbon constrained world, there are large economic incentives to develop nuclear power plants with heat storage to provide dispatchable electricity to the grid (Fig. A.1)—replacing fossil fuels in this role. Heat storage is an order-of magnitude less costly than electricity (batteries, pumped hydro, etc.) storage. One operates the nuclear reactor at base-load. At times of low-electricity prices, heat is sent to storage. At times of high electricity prices, reactor heat and heat from storage is used to produce peak electricity. Today heat storage at the gigawatt-hour scale is deployed at some solar thermal power systems for this reason. Nuclear energy and solar thermal produce heat and thus many of the same heat storage technologies and power conversion systems can be used. For assured peak power capacity in the event that heat storage is depleted, there is the option to add a combustion furnace burning natural gas, biofuels or ultimately hydrogen. Such a furnace provides assured peak capacity but would be seldom used because heat storage usually provides the peak capacity. Such furnaces have low capital costs. There is the option to send low-price electricity to heat storage systems where firebrick or crushed rock is heated to high temperatures and later air is blown through the firebrick or crushed rock to provide hot air to the combustion heater.

Program:     ANP : Advanced Nuclear Power Program

Type:     TR 

RPT. No.: 184